Calcium exchange in isolated cutaneous epithelium of toad Bufo marinus

The Ca content of isolated cutaneous epithelium of toads (Bufo marinus) was 5 mmol/kg wet wt (compared with approximately 300 mmol/kg wet wt for intact skin), of which approximately 1.7 mM is not readily exchangeable with external 45Ca. After incubation in a solution containing 45Ca, loss of the accumulated isotope in an isotope-free medium is almost complete in 2 h. This efflux or washout is reduced by the presence of external Ca- and Na-free media and by La. Loss of Ca from the epithelium may thus reflect the presence of several mechanisms including a Ca-Ca exchange and a Ca-Na exchange. The effect of La (2 mM) was greater than that of a Na- and Ca-free medium, possibly reflecting the presence of an uncoupled Ca extrusion or extrusion by a Ca-ATPase (pump) mechanism. Drugs (ouabain and amiloride) that, respectively, increase or decrease levels of internal Na had no significant effects on efflux or accumulation of Ca. Vasopressin was also without such effects on Ca.